It has hitherto been known that a substance consisting of silica gel physically carrying a polysaccharide, such as cellulose, amylose or a derivative thereof, is useful as a separating agent for use in chromatography, in particular, as a separating agent for optical resolution.
However, due to its poor solvent resistance, the substance suffers from the drawback that a usable eluent is limited at the time when it is to be used in liquid chromatography, or the like. In addition, it is not possible to fully utilize the usefulness of the polysaccharide. There is also a limitation in solvents usable for the washing of contaminated columns, which can be a cause for the deterioration of columns.
In order to solve such problems, it has been proposed to use a compound in which a polysaccharide is chemically bonded to silica gel. However, in this case, it is not possible to select the site at which the chemical bonding to silica gel takes place. This exerts influences on the higher structure of the polysaccharide per se and the usefulness of the polysaccharide is diminished. In addition, there occurs still another problem that the silica gel compound thus obtained shows a big difference in quality since the bonding does not take place at a specific site.
The present inventors have carried out investigations on the use of a separating agent of the structure wherein silica gel is used as a porous carrier and polysaccharides are chemically bonded to the inner and outer surfaces of the pores of the silica gel at the reducing terminals of the polysaccharides. The present inventors have lactonized the reducing terminals of oligosaccharides and performed a reaction of the lactonized product with, for example, 3-aminopropyltriethoxysilane, to obtain a product containing a saccharide chain chemically bonded via an amide bond to a silane agent, as shown by the following Formula A: ##STR2## (wherein Rb represents a substituted or unsubstituted methylene group, a substituted or unsubstituted phenylene group or a group containing covalently bonded hetero atom(s); m.sub.2 represents an integer of from 1 to 20; m.sub.3 represents an integer of from 2 to 9; and n represents an integer of from 0 to 3, preferably 0). Part of the silane agents may be in a polymerized state.
The present inventors have also developed a method of polymerizing saccharide chains and succeeded, by using the method, in polymerizing the saccharide moleties of the compound represented by Formula A to an arbitrary polymerization degree by an enzymatic reaction using the compound as a primer. Further, the inventors have succeeded in obtaining compounds represented by Formula B set forth below, by allowing a polysaccharide derivative of a silane agent obtained by an enzymatic synthesis to bind to silica gel at the silane moiety. ##STR3## (wherein Z represents a member selected from the group consisting of the surface of a porous carrier, a halogen atom, an alkyl group, an alkoxy group, a phenyl group, a silane agent and a saccharide-bonded silane agent; m.sub.1 represents the number of monosaccharide units, which may be in the range of from 10 to 500 on average; and Rb and m2 have the same meanings as defined above).
The compounds represented by Formula (1) according to the invention have been obtained by substituting part or whole of the hydroxy groups in the saccharide moiety of the compound represented by Formula B with, for example, an isocyanate derivative, or the like. ##STR4##
Alternatively, the compounds represented by the above Formula B have been obtained in the following manner: The reducing terminal of an oligosaccharide is oxidized to a glucanate, and its saccharide moiety is polymerized to an arbitrary degree of polymerization with the action of an enzyme, using the glucanate as a primer. An acid is added to the resulting reaction mixture to effect lactonization. The lactonized polysaccharide is then allowed to bond via amide bond to a surface-treated silica gel having amino groups on its surface.
The compounds represented by the above Formula (1) have also been obtained by substituting part or whole of the hydroxyl groups in the saccharide moiety of the compounds of Formula B obtained as above with, for example, an isocyanate derivative, or the like.
In the thus synthesized compounds of Formula (1), saccharides are chemically bonded via a silane agent to the inner and outer surface of the pores of a porous carrier, such as silica gel, only at the 1positioned carbon in the reducing terminal of the saccharide moiety. It has been found that the novel compounds are capable of solving the above-mentioned problems, and the present invention has been completed on the basis of the finding.